Internal combustion engines have a cylinder block and at least one cylinder head connected together at their mounting faces to form the cylinder. The cylinders further have cylinder bores wherein pistons or cylinder linings reside. Within the cylinder bores, mobile pistons reciprocate axially along the guide to form the combustion chambers of the internal combustion engine.
During the charge change, the combustion gasses are expelled via outlet openings of the cylinders and the combustion chambers are re-filled with fresh mixture or charge air via inlet openings. To control the charge change, an internal combustion engine includes control elements and activation devices designed to activate the control elements. For example, in four-stroke engines reciprocating valves are almost exclusively used as control elements to control charge change during operation of the internal combustion engine, and to execute an oscillating stroke movement that opens and closes the inlet and outlet openings. The valve actuating mechanism that moves the valves, including the valves themselves, is commonly referred to as the valve gear. A typical cylinder head is designed to receive the valve gear.
Example cylinder heads known in the art have at least partly integrated inlet channels (e.g. inlet pipes) that lead to inlet openings and outlet channels (e.g. exhaust pipes) that connect to outlet openings of the cylinder head. Therein, when more than one exhaust pipe from the cylinders is present, the number of pipes present may be merged into a combined exhaust pipe, which is generally referred to as an exhaust manifold.
The inventors have recognized disadvantages with the cylinder head and exhaust manifold described above and herein disclose example exhaust pipes of a four cylinder engine that merge in stages such that at least one exhaust pipe from an outermost cylinder and at least one exhaust pipe from an adjacent innermost cylinder merge into a part exhaust pipe, wherein the two part exhaust pipes from the four cylinders formed in this way further merge into a combined exhaust pipe. Therefore, according to the present disclosure, advantages are offered since the total length, and hence the volume, of all exhaust pipes of the exhaust gas discharge system can be substantially reduced.
In one particular example based on exhaust pipes that merge in stages, the exhaust pipes merge into part exhaust pipes inside the cylinder head, which thus forms two part exhaust manifolds. The two part exhaust pipes then merge into a combined exhaust pipe outside the cylinder head so that the exhaust gas discharge system emerges from the cylinder head in the form of two exhaust gas outlet openings. For example, in the internal combustion engine of the present disclosure, the two exhaust gas outlet openings are arranged offset and spaced apart from each other along the longitudinal axis of the cylinder head so that the openings have substantially the same spacing from the mounting face of the cylinder head. This horizontal arrangement of the two outlet openings offers advantages with regard to achieving a low cylinder head height and an increased density of packaging within the engine system. However, it also relies on the two adjacent cylinders forming a group so the exhaust pipes are merged into part exhaust pipes. Furthermore, even if the exhaust pipes were to merge respectively into a part exhaust pipe forming a part exhaust manifold, wherein the outlet openings lie vertically above each other in the vertical direction, or in the direction of a cylinder longitudinal axis, the offset relative to each other may result in different spacings from the mounting face, which presents difficulties with respect to packaging of the engine system.
The present description of the approach to achieve the merging of the exhaust pipes at least partly within the cylinder head may offer several advantages. For example, integration of the part exhaust pipes in the cylinder head leads to a more compact construction of the internal combustion engine and a denser packaging in the engine bay. As such, a weight reduction of the internal combustion engine may be realized that leads to cost benefits during engine production and installation. Furthermore, the integration can have an advantageous effect on the arrangement and operation of an exhaust gas post-treatment system provided downstream in the exhaust gas discharge system. For example, in some embodiments, a reduced travel length of the hot exhaust gasses to various exhaust gas post-treatment systems provides little time for the exhaust gasses to cool before treatment, which may enable an exhaust gas post-treatment system to reach its operating temperature or trigger temperature as quickly as possible, in particular after a cold start of the internal combustion engine. In this context, extensive integration of the exhaust manifold in the cylinder head is advantageous and the aim of the present disclosure is to minimize the thermal inertia of the partial piece of the exhaust pipes between the outlet opening at the cylinder and the exhaust gas post-treatment system, which may be achieved by reducing the mass and length of the partial pieces.
In one particular example, an internal combustion engine charged by an exhaust gas turbocharger, the turbine may be arranged as close as possible to the outlet, for example, the outlet openings from the cylinders. This may be done in order to make optimum use of the exhaust gas enthalpy of the hot exhaust gasses, which in some instances is determined by the exhaust pressure and temperature, to thereby achieve a rapid response behavior of the turbocharger. As described already, when the system is implemented according to the present disclosure, the thermal inertia and volume of the pipe system between the outlet openings of the cylinders and the turbine may be substantially minimized, which results from extensive integration of the exhaust manifold within the cylinder head.
The method described further utilizes the circumstance that modern internal combustion engines are increasingly equipped with liquid cooling systems. When liquid cooling is present within the engine system, the internal combustion engine or cylinder head may, for example, be fitted with at least one coolant jacket, or in another example, coolant channels designed to carry coolant through the cylinder head. Implementation of liquid cooling systems often entails a complex structure of the cylinder head construction. Therefore, integration of the part exhaust pipes within the cylinder head makes it more difficult to arrange or form a sufficiently large coolant jacket volume in cylinder heads under a high thermal and mechanical load. However, because the exhaust manifold is largely integrated into the cylinder head, the manifold may be cooled by targeted cooling provided in the cylinder head and so may not be produced from materials with a high thermal load capacity, which are increasingly cost-intensive.
In particular, charged internal combustion engines are subject to a high thermal load and therefore impose high cooling restrictions. For example, the heat released by the exothermic chemical conversion of fuel combustion is dissipated partly to the cylinder head and cylinder block via the walls delimiting the cylinder chamber, and partly to other components and the environment via the exhaust gas flow. Therefore, to keep the thermal load of the cylinder head within a desired operating range, cooling is achieved in a targeted manner inside the cylinder head by means of liquid cooling and forced convection. The heat may then be dissipated to the coolant in the interior of the cylinder head. The coolant is further delivered by means of a pump arranged in the cooling circuit so it circulates throughout the coolant jacket. As such, the heat dissipated to the coolant is discharged from the interior of the cylinder head and extracted from the coolant in a heat exchanger. In view of the above, the object of the present invention is to provide a liquid-cooled internal combustion engine according to the present disclosure, which is optimized with regard to liquid cooling.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.